I still think that the JVC cam is the smallest of the lot at ready to use specs - 135g and shorter than most of the others in that form-factor.
Strangely i cant find *any* size specs for the Hero3+ housing size, so cant compare, but the hero mounting screws etc would add to the size, whereas the JVC has the tripod mount built in.
My jacket has small pockets, but I carry my JVC in my left jacket pocket, along with my goggles pouch. Extendable pole fits in my pants pocket, and i am good to go whenever i need to.
I also just read about the latest Sony. HDR-AS100V, which is also waterproof without a housing, and that is only 90g or so. I think its the same height/length as the JVC, but a bunch skinnier. Someone here said the Sony cameras dont capture snow very well though, turning it blueish...